In a wobble plate type compressor of the kind described in U.S. Pat. No. 4,042,309, the rotor is wedge-shaped and is sandwiched between the wobble plate and a front plate of the compressor which rotatably supports the drive shaft. The wobble plate compressor is small in volume and is suitable for automotive air conditioning systems.
The compressor shown in the above-identified U.S. patent is provided with two anti-friction thrust bearing assemblies having a pair of annular race members and a rolling element cage assembly sandwiched between the annular race members. One of the thrust bearing assemblies is disposed between the front end plate of the compressor housing and the rotor to take up thrust load on the rotor, and the other bearing assembly is disposed between the rotor and the wobble plate. As a result, frictionless driving of the wobble plate is provided.
A plurality of radial projections are formed on the surface of the annular race members and are received in a plurality of depressions formed in the front end plate, the rotor and the wobble plate, which limit the radial movement of the annular race members. When thus positioned, a small radial gap exists between each annular race member and each depression so that appropriate play is provided between the race member and the supporting structure, i.e., the rotor, wobble plate and front end plate.
Typically in a wobble plate type compressor, a rotation-preventing mechanism for converting the rotating motion of the rotor to wobbling motion of the wobble plate is provided in the form of an angular motion converting mechanism. However, it is difficult with these kinds of motion converting mechanisms to obtain an angular motion conversion with perfectly regular angular velocity. Thus, when the drive shaft rotates at high speeds, a fluctuating torque occurs which tends to cause radial vibration of the wobble plate. This fluctuating torque is increased by the fluctuating torque which results from compressing refrigerant gas. When the fluctuating torque exceeds a certain value, the wobble plate begins a radial vibration, the amplitude of which is determined by the amount of play in the rotation-preventing mechanism.
In the above-mentioned compressor (shown in U.S. Pat. No. 4,042,309), the annular race member disposed on the wobble plate will also begin to vibrate radially with the radial vibration of the wobble plate. As a result, and because only a small radial gap will normally exist between the annular race member and the wobble plate, the radial projections formed in the annular race member collide with the depressions formed in the wobble plate. Thus, after several hours of operation, the radial projection of the annular race member, which is made of steel, may thust through a side wall of the depression of the wobble plate, which is made of aluminum alloy, or the radial projection may be broken, causing serious damage to the wobble plate and bearing assembly. In addition, the noise that results from the collision between the radial projection and the depression is not negligible.
These problems become more noticable depending upon the extent to which the rotation-preventing mechanism achieves angular motion conversion with irregular angular velocity. In this regard, use of a rotation-preventing mechanism which includes a guide rail element disposed in the compressor housing and a slider element slidably disposed onto the guide rail element (such as shown in U.S. Pat. No. 3,552,886) will result in more irregular angular velocity than a rotation-preventing mechanism which includes a pair of intermeshing gear-like elements (also shown in U.S. Pat. No. 3,552,886). Yet, the former rotation-preventing mechanism is necessary for a wobble plate type variable displacement compressor of the type shown in U.S. Pat. No. 4,073,603. For this reason, solving the above-mentioned problems becomes particularly important.